Post on 04-Jan-2016
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Introduction to the Common Gateway
Interface(CGI)
Instructor: Joseph DiVerdi, Ph.D., M.B.A.
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Examples
• Web Clock
Changes from one viewing to another
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Examples
• Simple Survey
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Examples
• Simple Game
CSU - DEOIntroduction to CGI - Fort Collins, CO
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CGI Examples
• Quiz
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Examples
• Search Engine
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Examples
• Database access
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Overview
• CGI stands for Common Gateway Interface– It is a Specification Which Permits The Web
Server Program to Communicate With Other Programs That Are Running On The Server
• Web Server Only Knows How to Serve Up HTML Pages• CGI Enables Server to Interact With Other Programs
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Overview
• Operation is as follows:– Client Requests a Document– Server Recognizes That Document is a Program– Server Executes Program
• Supplies Data to Program Obtained From Client Request
– Server Receives Program Output– Server Returns Document to Browser– Client Renders Document
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Dynamic Image Inclusion
<HTML>
<HEAD>
<TITLE>Digital Clock Demo</TITLE>
</HEAD>
<BODY>
<IMG SRC="/cgi/digital_clock.pl">
</BODY>
</HTML>
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Examples
• Web Clock
Changes from one viewing to another
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Overview
• There are Few Restrictions on What Programming Language is Used in CGI Programs
• Perl, Java, Visual Basic, AppleScript, Shell, C++, ...• Perl is the Most Popular Language In Use
• CGI Defines The interface Between The Web Server & The Program– In Both Directions
• Web Server --> Program• Program --> Web Server
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI In Brief
CSU - DEOIntroduction to CGI - Fort Collins, CO
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Uses of CGI
• Page Serving is Not Limited To Previously Written Documents
• Web Pages Can Created On-The-Fly– Can Be Based on The Viewer's Input
• Collect Viewer Comments• Respond to Responses
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Dynamic Page Content
• Page Created Dynamically Via CGI Program• Page With Server Side Includes (SSI)• Page With Embedded Call to CGI Program
– The Result is Still an HTML Page– Viewer's Browser Just Sees HTML– CGI Interaction is Behind The Scenes
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Database Interaction
• Web Interface to Relational Database Management System (RDBMS)
• CGI Program is Required to – Decode Viewer Input– Assemble Query– Send Query to Database– Process Data Returned From Database– Create Return HTML Document
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Gateway to a Database
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Setting Up For CGI Programs
• Create cgi directory in html directory– CaSe iS vErY iMpOrTaNt!
• Ensure cgi directory has 755 permission• Programs must be placed in this directory
– Server is configured only to execute from there• Programs placed in and viewed from other directories
will not execute and the program contents will be rendered on the browser
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Using CGI Programs
• Ensure CGI programs have 755 permission• Always test program with telnet client FIRST!
– Login to your account– Navigate to the html/cgi directory– Check if the program executes successfully
env.cgi
• Then test using Browserhttp://linus.ulltra.com/~my_account/cgi/env.cgi
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Simple Shell Program
• Create a file "env.cgi"#! /bin/sh
echo "Content-type: text/html"
echo
env
• Remember...– CGI programs can be written in many languages
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Simple But Useful Program
• Create a file "simple.pl"#! /usr/bin/perl -w
print "Content-type: text/html\n\n";
print "Hello, CGI Programmer!<BR>";
exit;
• Save file in cgi directory• Ensure program has 755 permission• Test using telnet client• Test using browser
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
More Useful Program
• Modify the file "simple.pl"#! /usr/bin/perl -w
print "Content-type: text/html\n\n";
print "Hello, CGI Programmer!<BR>";
print "The current time is ", scalar localtime, "<BR>";
print "You are using the computer: ", $ENV{'REMOTE_HOST'}, "<BR>";
exit;
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Form Processing
• Client Requests a Form
CSU - DEOIntroduction to CGI - Fort Collins, CO
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CGI Form Processing
• Client Renders Form
CSU - DEOIntroduction to CGI - Fort Collins, CO
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CGI Form Processing
• Viewer Fills in Form• Client Sends Form to Server
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Form Processing
• Client Sends Data to Server– Uses POST Method in HTTP Request
POST /cgi/formmail.pl HTTP/1.0
Host: xtrsystems.com
... more headers here ...
ice_cream_flavor=chocolate
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Form Processing
• Server Recognizes URL– URL Points to CGI Program
• It knows because of the directory in the URL
/cgi/formmail.pl
• Server Executes Program– Supplies Form Data to Program
• Form Data Received From POST Request
"ice_cream_flavor=chocolate"
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI In Brief
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Form Processing
• Program Performs Some Work– Some Combination of the Following
• Stores Submitted Data in Database• Creates e-mail Message From Submitted Data
– Always Does This• Creates HTML Thank You Page
• Sends Program Output to Server– HTML Thank You Page is Program Output
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI Form Processing
• Server Sends HTML Document to Browser• Client Renders HTML
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
CGI and Form Processing
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Executing CGI Programs
• CGI Programs Are Just Like Other Resources– Can Reside on Your Host
• The Host With the Server
– Can Reside on Some Other Host• With the Owner's Agreement• Without the Owner's Agreement
• Unlike Other Resources– Must Reside in Specific Directories on Each Host
• Directory Selected by Webmaster or Site Administrator
– Much Harder to Write than HTML Documents
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Hands On Work
• Create an Ice Cream Survey Form Page– Include the following HTML:
<FORM METHOD=POST ACTION="http://xtrsystems.com/cgi/formmail">
• You are using the formmail program– Executing On the xtrsystems.com Server Host
CSU - DEOIntroduction to CGI - Fort Collins, CO
Copyright © XTR Systems, LLC
Using Your own Programs
• Install formmail.pl in Your Own Account– Download From Course Materials Page– Upload to cgi Directory– Check Program Permission– Modify Form HTML– Test as Described Earlier– Modify Program
• Be Very Careful
– Have Fun